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94 the part of the Federal Government in the construction of any route conforming to the interregional highway system as it is finally designated.

Prefatory to the standards proposed, the Committee offers the following fundamental recommendations:

1. The interregional highway system, as it is hereafter constructed or improved, shall provide or allow for the subsequent provision of facilities capable of serving safely and efficiently a mixed traffic of passenger automobiles, motor busses, and motor trucks, and tractor-trailer and semitrailer combinations, of a volume of each of the constituent elements estimated to be that which will exist 20 years from the date of construction.

2. All roadways and structures built on the interregional system shall provide, either in their immediate design or feasible modification thereof, for the passage and support of vehicles and combinations of vehicles of the following dimensions and weights, in the frequency and distribution of such dimensions and weights to be expected 20 years from the date of construction:

Gross weight on any vehicle or combination of vehicles according to the formula.

3. For purposes of the design of highway facilities and the application of standards and conditions hereafter recommended, all sections of the interregional system in or approaching a city or town and at least 1 mile long, along which intersecting roads or streets average one-quarter mile or less apart, shall be considered as urban sections, regardless of their locations within or without the corporate limits of cities. All other sections of the system shall be considered as rural sections, regardless of their location within or without the corporate limits of cities.

4. All rural sections of the system shall be designed at all points and in all respects for safe travel by passenger vehicles at a speed of not less than 75 miles per hour, and by trucks and tractor combinations at a speed of not less than 60 miles per hour in flat topography. In more difficult terrain the speed for which the highway is designed may be reduced; but in no case to less than 55 miles per hour for passenger vehicles and 35 miles for trucks and tractor combinations in mountainous topography. All rural sections shall provide a sufficient number of traffic lanes and other facilities so that at no time, except during infrequent peak hours, will it be necessary because of the interference of other vehicles to reduce the average running speed to less